The Mazda RX-4 front and rear turn signal bulbs both utilize a 1157 size bulb for proper illumination. The replacement chart covers 1974 through 1978 model years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 1157 is the sole turn signal bulb type listed for the Mazda RX-4 across all covered model years, applying to both front and rear positions from 1974-1978.
The 1157 is a dual-filament bulb, meaning it houses two separate filaments within a single envelope, allowing it to serve both a high-intensity function and a lower-intensity function from one unit.
The two filaments operate at 21W and 5W respectively, with the higher wattage filament handling the active turn signal flash and the lower wattage filament typically serving a parking or running light role.
The 1157 operates on a 12V electrical system, consistent with standard automotive electrical architecture of the era.
The bulb uses a BAY15d bayonet base, which is an offset twin-contact base. The offset pin arrangement is a deliberate anti-misalignment feature, preventing the bulb from being seated incorrectly in the socket.
The 1157 conforms to ANSI standards and carries recognition in both the United States and Canada, reflecting a standardized specification shared across North American markets.
Because the 1157 is uniform across all five model years and both front and rear positions on the RX-4, a single bulb type covers the full turn signal fitment for this vehicle.
The BAY15d base of the 1157 is not interchangeable with single-contact bayonet bases such as the BA15s, and substituting a single-filament bulb in a dual-filament socket would result in incomplete circuit function.